To suppress the atmospheric diffusion of particles contained in the exhaust gas of diesel engines, in recent years, various apparatuses are being developed for mounting in the exhaust system of diesel engines for after-treatment of diesel particulates in the exhaust gas. There is an exhaust gas treatment apparatus of this type that is in the course of becoming of practical utility, having a configuration that includes a filter for trapping particulates contained in exhaust gas discharged from the diesel engine when the exhaust gas passes through the exhaust path. With this type of exhaust gas cleaning apparatus, particulates trapped by the filter gradually accumulate, loss caused by elevation of exhaust resistance gradually increases, and ultimately the filter becomes clogged. When the quantity of the accumulated particulates in the filter used in the exhaust gas cleaning apparatus reaches a prescribed level, the filter is heated to burn the accumulated particulates and regenerate the filter, and the filter is re-used.
Hereupon, burning particulates to regenerate the filter leaves a residue of ash in the filter, and since the residual ash accumulates with each filter regeneration, as the number of regenerations builds up, the residual ash in the filter obstructs the outflow of the exhaust gas. Since before, therefore, the before and after differential pressure which is the differential pressure between the filter inlet pressure and outlet pressure, is measured at the completion of each filter regeneration, and the measured before and after differential pressure value of the filter is used as a basis to estimate the quantity of residual ash in the filter, and the filter life is determined in accordance with the result of the estimation.
However, with a configuration in which the residual ash quantity is estimated by measuring the before and after differential pressure of the filter, in cases where, after starting the filter regeneration process, for some reason or other the regeneration process is interrupted, leaving unburned particulates in the filter, even if the before and after differential pressure of the filter is measured after the completion of the regeneration process, residual ash quantity cannot be measured accurately due to the unburned particulates. This being the case, it frequently has been impossible to determine correctly the time to replace the filter.
An object of the present invention is to provide an exhaust gas cleaning apparatus that is able to resolve the above-described problems of the conventional technology.
An object of the present invention is to provide an exhaust gas cleaning apparatus that makes it possible to accurately ascertain the quantity of ash remaining in a filter.
An object of the present invention is to provide an exhaust gas cleaning apparatus that makes it possible to replace filters at a suitable timing.